FIG. 1 is an illustration of a differential volume element 14 in a target 16 being imaged using a B-mode ultrasound imaging technique. A transducer 10 emits a pulse, such as a pulse signal, for example, from each of a linear array of transducer elements 12(1-N) with each emitted pulse delayed by a predetermined amount. Depending on the delay utilized, an acoustic beam of energy can be aimed in a direction θ and focused onto a target 16. When the acoustic energy is reflected, such as results from a change in impedance in the target 16, some of the acoustic energy is reflected back to the transducer elements 12. By measuring the time between emitting and receiving the pulse at each of the various transducer elements 12, an amplitude of the echo such as from volume element 14 can be calculated.
By controlling the delays for a plurality of pulses, a two dimensional slice of the target may be imaged by scanning radially back and forth across a plane extending outward from the transducer 10. Such scanning, referred to as B-mode scanning, returns a reflectance value for a range of distances r across an angle Ω. When the reflectance value for all points in the plane corresponding to a distance r at an angle Ω are translated into planar coordinates, such as along the illustrated orthogonal axes X and Y, for example, an image is formed of pixels having an X and Y coordinate with the value of each pixel related to an amplitude of the echo received from a corresponding differential volume element 14 of the target 16.
Typically, the images formed from B-mode ultrasound imaging are grayscale images, where the brightness of each pixel is proportional to the magnitude of the echo received from the corresponding point in the imaged target. Because tissue is comprised of different features having different densities or compressibilities, ultrasound images of human tissue can be interpreted to determine the relative and absolute location and the acoustic reflectivity of different tissue types such as bone, soft tissue, tendons, and the like. While useful for many applications, traditional ultrasound images based upon the magnitude of a reflected signal are often times not of sufficient clarity to permit robust analysis.
It would be advantageous to generate a metric from traditional ultrasound emitted and received pulses that provides additional information regarding the nature of a target 16.